Any time I encountered John Hume, he always came across as a slightly dishevelled academic - somewhat crumpled and preoccupied, preoccupied by higher things than straightening his collar.

But once engaged in conversation, there was nothing unfocused about this clever, singular man.

He had - still has - the instant recognition factor. The stories about him having chats with random strangers met on the street are legion. I mean a proper dialogue, not just a nod or a handshake: he never forgot to give individuals their due respect.

Odd, how such a statesman - perhaps the finest produced by Ireland in the 20th century - never held the high public office for which nature fitted him. He was a founding member of the SDLP, of course, going on to lead the party for more than 20 years. And he has been garlanded by honours including the Nobel Peace Prize in 1998, while in 2012 he was made a papal knight. But still there is a sense of a man who sacrificed much, perhaps even his party, in his pursuit of the holy grail. And what a goal he had in his sights. Nothing less than peace.

Despite setbacks on that decades-long journey, John's moral compass pointed in one direction only throughout his life: non-violence. It never wavered. He said that a dead person couldn't step back out of their coffin, and it seems to have been the irrevocable finality of death - so many graves filled by innocent victims of the Troubles - which spurred him on.

His sustained efforts led to the 1994 IRA ceasefire, followed by the loyalist paramilitaries' ceasefire, and paved the way for the Good Friday Agreement of 1998. Who knows if the peace process could have happened without him? Certainly, he was integral to it, as well as a colossus of persistence and conviction throughout the darkest days of the Troubles. But he has been absent from the public spotlight for a number of years now, and a generation is reaching maturity which may not realise the full extent of his contribution, the true gift of his integrity.

A reminder came last week via the voice of Pat Hume, his wife of 55 years and mother of his five children, describing on RTÉ radio's Sunday With Miriam how dementia has attacked that fine mind. A mind which had grasped that there could be no lasting solution unless all the key players in Northern Ireland sat at the negotiating table. That mind is now in a state of severe memory malfunction. But even if he forgets the details of his eventful career, we should not allow ourselves a similar omission. That's why books about him matter: such as a new one, John Hume - Irish Peacemaker, published by Four Courts Press.

"Bloodshed for political change prevents the only change that truly matters: in the human heart," he said once, in what sounded like a personal credo. At times, peace must have seemed like a mirage in a desert of polarisation. But if he lost heart privately, in public he remained resolute. A way past the obstacles would be found. Now aged 78, John laid the foundations over many difficult years for the peace process.

Slowly, slowly, nudging and encouraging, he advanced the idea of the principled compromise rather than compromised principles.

"Difference is an accident of birth, and it should therefore never be the source of hatred or conflict. Therein lies a most fundamental principle of peace: respect for diversity," he said at the Oslo ceremony where he shared the Nobel Prize with David Trimble.

In fact, John is the only person to have won three peace prizes: the Nobel, Gandhi Peace Prize and Martin Luther King Award. He is also chest-deep in honorary doctorates.

But he has said he is proudest of his role as a founding member of Derry's Credit Union movement.

Before its inception, people from poor or working-class backgrounds couldn't borrow from banks, but the movement offered an alternative to that discrimination.

John is a flesh and blood man, rather than a plaster saint, and always enjoyed a few drinks and the opportunity to sing 'The Town I Love So Well' at social gatherings.

But the son of a civil servant was drawn to the priesthood initially. He studied at Maynooth for several years before returning to his native Derry as a teacher.

There, he became prominent in the civil rights movement, and later became an elected representative in various parliaments.

In 1977, following representations from John, four key Irish-Americans joined forces to condemn the support for Noraid, the Provisional IRA's fundraising arm.

They were Senator Ted Kennedy, House of Representatives Speaker Tip O'Neill, Senator Daniel Patrick Moynihan of New York, and Governor Hugh Carey of New York. As Senator Kennedy put it, their mission was "to insist that dollars from America must never be used to kill innocent men and women and children in Northern Ireland".

These 'Four Horsemen' acted together on numerous occasions to advance a peaceful resolution in the North, and John Hume planted the seed.

Another significant intervention came from him when the Irish and British governments issued the Downing Street Declaration in 1993.

Soon after, President Bill Clinton was faced with a crucial decision: should he grant a visa to Gerry Adams to visit the United States? The British government was against it. But others, including John, advised that it would lead to the guns being silenced. President Clinton agreed to the visa, the IRA ceasefire followed, and Northern Ireland's fortunes took a turn for the better.

John's stance was not universally welcomed, although he argued that he was seeking to convince Republicans to abandon violence - even his own party struggled at times with his willingness to put his reputation on the line to lay the groundwork for peace talks.

Advocates of an ill-judged newspaper campaign in the early 1990s, at a sensitive time during negotiations and a backdrop of IRA bombs, argued that it was imply subjecting John Hume's actions to a valid and rigorous examination.

However, the sustained barrage looked suspiciously like ad hominem attacks.

Inevitably, those attacks took a personal toll on John but he never let them stand in the way of progress.

When the power-sharing executive at Stormont was formed, he stood aside to let his number two Seamus Mallon enter as Deputy First Leader. He was rumoured to have a testy working relationship with David Trimble, the inaugural First Leader.

If so, once again he was putting the national interest first. Ted Kennedy said of him: "He has been a constant voice of reason, an often lonely champion of non-violence, a stalwart advocate of peace."

Pat, however, has been by his side throughout the good times, and the bad.

The couple were photographed just last month, his attentive wife holding his hand at playwright Brian Friel's funeral in Glenties, Co Donegal.

It's easy to forget how many obstacles John Hume overcame, and how it was only towards the end of his career that he had the wind at his back - for most of the time, he had to swim against the tide.

Lucky for us that he proved to be not just a visionary but a strong swimmer.